The present invention relates to analysis and evaluation of a fluid or particle stream and more particularly to a device for observing and analyzing a powder stream from a coaxial powder feed nozzle of a laser welding apparatus to provide better control of laser welding parameters during a laser welding operation.
Laser welding apparatuses with coaxial powder feed nozzles are receiving wider application in industrial production environments, such as the manufacture of gas turbine engines and the like. An example of a laser apparatus with a coaxial powder feed nozzle is disclosed in U.S. Pat. No. 4,724,299, entitled "Laser Spray Nozzle and Method" issued on Feb. 9, 1988, to Hammeke.
To provide acceptable weld integrity, particularly in the gas turbine engine manufacturing industry, it is important that the powder is fed from the coaxial feed nozzle in a consistent uniform flow pattern to provide welds with minimal or no voids or other defects. Unacceptable weld joints can result because of nonuniform or asymmetrical distribution or shape of the powder stream exiting the coaxial powder feed nozzle.
In order to better understand and control the dynamics of the laser welding operation when using a coaxial feed nozzle, the ability to observe and analyze the powder stream exiting the nozzle including the interior portion of the stream is desirable.
A current method used to observe and analyze the powder stream is to direct a beam of white light of sufficient intensity on the powder stream so that the powder stream is clearly visible to the human eye. The gas flow rate of the carrier gas may then be adjusted until the visible powder stream shape or cone of the stream exhibits a desired shape which has proven to provide acceptable laser welding results. A disadvantage to this method, however, is that only the overall shape of the outer portion of the powder stream is discernable. The interior profile of the stream is masked by the reflection of the light from the outer portion of the powder stream cone. The shape or profile of the interior portion of the powder stream has been found to be of importance, if not more importance than the shape or profile of the exterior portion of the stream. This is because of the interaction between the laser beam and the powder stream during a welding process.